Rotary scraping devices having a central hub and a plurality of oxtwardly extending spring-like fingers for scraping engagement with a work surface are known in the art. A primary example for such device can be found in U.S. Pat. No. 3,958,294 to Thompson. The rotary scraper disclosed in the Thompson patent comprises a hub having a pair of spaced apart disc shaped plates connected by a plurality of rods, called pivot shafts, equally spaced along the outer periphery of the hub plates. The hub also includes a central drive shaft which interconnects the two hub plates and extends to the exterior thereof. Such shaft can be connected to a rotational drive means, such as a power drill, for imparting the necessary rotational movement to the hub.
Each pivotal shaft carries thereon a plurality of generally L-shape wire fingers wound by means of a coil thereabout. According to the Thompson patent a further series of rods, referred to as restraining shafts, are disposed between each of the pivot shafts to engage the inside end or short leg of each wire finger and thereby limit the arcuate travel of the outside ends (the scraper portion) of the wire fingers. In this manner, the wire fingers which extend exteriorly of the hub are restrained from extending into a radial position so that they must contact the work surface at an angle. In actual practice, the device manufactured by Thompson is somewhat different than that disclosed in his patent. In the actual device there are no restraining shafts per se, and the inner ends of the wire fingers are free to pivot between the central drive shaft, which serves as a common restraining shaft, and an adjacent pivot shaft. Since the wire fingers extend unsupported from their coils their flexibility or stiffness depends on the thickness of the material and strength of the spring coil. Thus, Thompson provides scrapers of different finger gauges for different purposes. According to Thompson the material to be removed from a surface is loosened by the striking of the fingers thereagainst rather than digging into the surface. The material is then lifted off by the unflexing of the finger as pressure is relieved by the rotary travel of the scraper.
While the concept of the Thompson rotary scraper is meritorious, the actual construction has several disadvantages, which impair its operation and limit its useful life. Although the wire fingers are pivotally movable, the limit of such pivotal movement is such that they are maintained within an angular range which permits rotation of the scraper in one direction only. If the device is used otherwise, it will cause extensive damage to the work surface through gouging. This is particularly true where a large gauge wire is utilized for the fingers.
In addition, it has been found that there is tendency for the wire fingers in the Thompson device to deform and bend out of shape through excessive use, where a high pressure is applied to the rotary scraper during use to remove material from or polish a particularly hard work surface.
Finally, and most importantly, the uses to which a Thompson scraper can be put depend to a great extent on the thickness or gauge of the fingers. Fine gauge fingers can not always be effectively used on hard work surfaces having difficult to remove material, and coarse gauge fingers tend to gouge or mar a relatively soft surface.